The present invention relates to technology for improving conversion efficiency of synchronous rectification DC-DC converters and further to technology whereby in a switching regulator with a reverse current prevention function for detecting a reverse current and controlling a transistor for synchronous control, power loss is reduced while the reverse current prevention function is working and conversion efficiency is thus improved, and more specifically to technology which is effective for a semiconductor integrated circuit for controlling a switching regulator, and an electronic component for power supply (power supply module) and a power supply device which incorporate the same.
One type of DC-DC converter is a synchronous rectification switching regulator. In the synchronous rectification switching regulator, a main switching device is provided in a path in which current flows from a power supply to a load through a coil (inductor) and the current to the load is controlled by turning on or off this switching device and also a synchronous rectification switching device is provided between the node of connection of the main switching device and the coil and the ground (grounding point) and power loss is reduced by turning it on or off complementarily to the main switching device.
This synchronous rectification switching regulator has a problem that, although power loss is small when the load is relatively heavy, power loss is large when the load is light. This is because while the load is heavy, a positive current, or current to the load, flows in the coil but while it is light, the direction of the current flowing in the coil is reversed and a negative current (reverse current), or current which flows through the synchronous rectification switching device to the ground is generated, resulting in power loss. In order to reduce power loss due to such a reverse current, an invention has been proposed in which a light load condition which could cause a reverse current to flow in the coil is detected and the synchronous rectification switching device on the ground side is turned Off upon such detection (for example, Patent Document 1: Japanese Unexamined Patent Publication No. 2000-092824).